Thermionic valve oscillatory circuits



March 4, 1941- c. L, FAUDELL 2,233,596

THERMIONIC VALVE OSCILLATORY CIRCUITS Filed July 7, 1957 dr/valeomzlxm SIG/V494 //vPur INVENTOR I (l/ARLFY [ISL/F FAUDELZ ATTORNEY Patented Mar. 4, 1941 PATENT OFFICE THERMIONIO VALVE OSCILLATORY CIRCUITS Charles Leslie Faudell,

Brentford, England, as-

signor to Electric 8; Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Application July 7, 1937, Serial No. 152,311 In Great Britain July 17, 1936 2 Claims.

This invention relates to thermionic valve oscillatory circuits and has particular reference to circuits for generating a saw-tooth voltage wave form for use in deflecting the electron beam of a cathode ray tube. The electron beam may be defiected by a field set up by electromagnetic coils through which a current having a saw-tooth wave form may be passed or electrostatic deflecting plates may be employed in which case a voltage having a saw-tooth wave form is applied to the deflecting plates. One plate may be held at a constant potential while the potential of the opposite plate follows that of the saw-tooth voltage wave form or saw-tooth voltages in pushpull relationship may be applied to the deflecting plates.

According to the present invention a thermionic valve circuit arrangement for generating voltages of saw-tooth wave form includes an Oscillator valve which serves to control a second oscillator valve, both valves being operatively associated with a circuit element or elements in such a manner that equal potentials of opposite phase are generated across said circuit element or elements. The said circuit elements may be constituted by two condensers one of which is arranged to be charged only when the second valve is rendered conductive. An oscillatory condition of the first valve initiated by a pulse applied to the grid circuit of said valve causes said second valve also to oscillate, the oscillatory condition of said first valve causing a condenser to be discharged simultaneously with the charging of a second condenser due to the oscillatory condition of said second valve.

In a particular circuit arrangement embodying the invention, an oscillator valve controls a second oscillator valve by means of a transformer coupling the anode circuit of the first valve to the grid circuit of the second valve, and the circuit includes a condenser having one plate connected to the anode of said first valve and charged through a resistance or choke coil connected to a source of potential and a second condenser shunted by a resistance or a choke coil, and having one plate connected to the cathode lead of said second valve and charged through the anode-cathode path of said second valve.

In order that the invention may be more clearly understood and readily carried into effect, a circuit for generating a voltage of saw-tooth wave form embodying the invention will now be describedby way of example with reference to the single figure of the drawing.

Referring to that drawing, the valve I operates as a blocking oscillator producing a voltage of saw-tooth wave form across a condenser 2 which is charged from a source of high tension voltage through a resistance 3. The grid-cathode circuit of valve 1 includes one winding 4 of a transformer, a condenser 5 and a variable leak resistance 6, this circuit determining the natural frequency of the saw-tooth oscillations produced by the valve I in the known manner of a blocking oscillator circuit as described for example in the specification of British Patent No. 235,254. Synchronizing signals which ensure the desired constancy'of frequency are applied to the grid circuit of the valve I at terminal I. A second transformer winding 8 is connected between the anode of the valve l and the resistance 3, and a third transformer winding 9 serves to couple the grid circuit of valve l to the grid circuit of a second blocking oscillator valve [0. The grid circuit of this Valve includes a condenser II and a leak resistance I2 and the anode-cathode circuit includes resistance l3 and a condenser M which is charged from a high tension source through the valve when that valve is conducting.

Terminals l5 and I6 are connected to the opposite deflecting plates of a cathode ray tube not shown in the drawing.

In operation of the circuit arrangement, an incoming synchronizing signal will initiate a burst of oscillation in the anode circuit of the valve l and the condenser 2, which is continually tending to be charged through resistance 3, is suddenly discharged. The burst of oscillations causes a current impulse to flow in the winding 8 and a voltage impulse is induced in winding 9 causing the valve I0 to become conductive and rapidly to charge the condenser l4. Grid current flowing in the valve lll due to the oscillatory impulse causes the plate of the condenser ll nearest the grid to become negatively charged with the result that the valve Ill ceases to be conductive. The charge in the condenser M then leaks away through resistance I3 and the charge in condenser I I leaks away through resistance I2. Simultaneously the condenser 2 is being recharged and when the point is reached at Which a succeeding synchronizing impulse is received the cycle of operation is repeated. It will be seen therefore that the saw-tooth voltage waves applied to the terminals I5 and I6 are in pushpull relationship, the voltage at one terminal rising while that of the other is falling.

In order that the time constant of the combination including resistance l2 and condenser II is appreciably greater than the time constant of resistance 6 and condenser 5, resistance I 2 may have a high value.

The invention is not limited to the particular arrangements described and modifications may be made within the scope of the invention. Thus, for example, in a modified circuit arrangement the anode of valve I may be connected to the anode of valve l instead of to the positive terminal of the high tension source so that the valves become oscillators in parallel. In this case the grid circuit of the valve I0 is arranged so that the time constant of H and I2 is appreciably longer than the time constant of 5 and 6 under the operating conditions, but the valve Ill is caused to synchronize with that valve by the oscillatory impulse which it generates.

A detailed modification may consist in replacing resistances 3 and [3 by choke coils. Again, while blocking oscillator valves have been referred to, it will be understood that other types of oscillator may be employed.

Among other possible modifications of the circuit described is the use of a single condenser instead of the two condensers 2 and M. In such a case, the opposite plates of the single condenser would be connected to the upper ends of the resistances 3 and I3 and also to the terminals l5 and Hi.

What I claim is: r 1. Means for producing push-pull saw tooth oscillations comprising a first and a second condenser in series with a connection point therebetween connected to ground and an output circuit connected across the two condensers in series, means for charging said first condenser substantially linearly, means for discharging said first condenser, means responsive to the operation of said discharge means for charging said second condenser and means ion discharging said second condenser substantially linearly.

2. Apparatus in accordance with claim 1, wherein said means responsive to the operation of said discharge means for charging said second condenser comprises a thermionic tube having said condenser connected in a current carrying electrode-cathode circuit of said tube.

CHARLES LESLIE FAUDELL. 

